1. Field of the Invention
The present invention relates to a light emitting module and, in particular, a light emitting module equipped with a phosphor layer that converts the wavelength of incident light and then radiates the wavelength-converted light.
2. Description of the Related Art
In recent years, use of semiconductor light-emitting elements, such as light emitting diodes (LEDs), has grown very quickly in automotive headlamps, general illumination and so forth. When white light is to be obtained using such semiconductor light-emitting elements, a light wave conversion member is generally provided in a position facing a light emitting surface of the semiconductor light-emitting element that emits light such as blue light, near-ultraviolet light or short-wavelength visible light. Here, the light wave conversion member converts light excited by the light-emitting element and then emits the converted light having a different wavelength. A device where a yellow phosphor, which is excited by blue light and then emits yellow light, is provided in a position facing an LED emitting the blue light, is known as an LED light emitting device of a white light-emitting type.
In order to obtain a white light with high color rendering properties, the wavelengths of three primary colors of light, namely blue, green and red light colors of light, are required. For this reason, the aforementioned white-light LED light emitting device, in which the blue LED and the yellow phosphor are combined, still has room for improvement in the color rendering properties. For the purpose of improving the color rendering properties, a white-light emitting lamp having a blue phosphor, a yellow phosphor and a red phosphor is proposed (see International Publication Number WO2008/096545, for instance). In this white-light emitting lamp, a light wavelength conversion member is first excited by light emitted by a semiconductor light-emitting element that emits light having a peak wavelength at 370 nm to 470 nm (both inclusive) and then emits white light.
The red phosphor, however, absorbs blue light and yellow light, too, whose wavelengths are shorter than that of the red light, and then emits the red light. Thus, as its optical path length is longer, the light emitted is more likely to be tinged with red color. Accordingly, it is possible that the red-tinged light may be more likely to be emitted from an emission surface of the light wavelength conversion member located far from a light emitting surface of the light-emitting element than in other emissions surfaces of the light wavelength conversion member located near the light emitting surface of the light-emitting element. Thus, it is strongly expected and requested that a light wavelength conversion member, which emits light such that the color of light emitted from the emission surfaces is uniform, be developed.